1. Field of the Invention
The present invention relates to a touch screen, and more particularly, to a touch screen which is operational based on optical characteristics.
2. Description of the Related Art
Touch screens have become increasingly popular because information that is pictorially provided to a user is preferred over hard keyboards or keypads. In addition, touch screens serve as an input device not only by pressing response prompts for inputting information, but also include menu buttons displayed on the screen by which the user can select specific information or character buttons where they can type specific characters. Accordingly, touch screens are used in various kinds of apparatuses such as machinery and equipment in industry, including but not limited to personal portable terminals, and automated-teller machines.
There are typically four types of touch screen classifications into which most touch screens can be largely classified, such as a resistance film type touch screen, an electrostatic capacity type touch screen, an ultrasonic wave reflection type touch screen, and an optical type touch screen using infrared light, etc.
For example, the resistance film type touch screens and the electrostatic capacity type touch screens determine a position on the touch screens that has been selected by a user based on resistance and electrostatic capacity. The resistance and electrostatic capacity are obtained when a point of contact is generated by the user touching a portion of the display.
In addition, the ultrasonic wave reflection type touch screens and the optical type touch screens function by the formation of an array, which is a kind of a lattice, of ultrasonic waves or rays. The ultrasonic wave reflection and optical type touch screen determine a position on their respective screen, which is selected by the user, based on the detection of rays on the lattice.
FIG. 1 is a schematic view illustrating a conventional structure of an optical type touch screen. Referring to FIG. 1, the conventional touch screen 100 has a lattice 130 formed by rays emitted from a plurality of light sources 111,122 to a plurality of light detectors 112, 121. The light detectors 112, 121 are arranged within a path corresponding one to one with a respective light source 111, 122, so that the conventional touch screen 100 determines the position selected by the user based on whether rays are detected on the lattice 130.
The light sources 111,122 are arranged on an adjacent surface positioned perpendicularly to the touch screen providing picture information, and the light detectors 112,121 are arranged so as to oppose the light sources 111,122, respectively. The light sources 111, 122 emit rays in the direction toward the corresponding light detectors 112, 121 so that the emitted rays form the lattice of rays 130. If the user puts a reflectable object, such as a part of the user's body or a pen, on a specific position on the lattice of rays 130, paths of the rays progressing to the corresponding light detectors 112, 121 are intercepted by the reflectable object. The result is that the rays that were intercepted by the reflectable object are not detected in the corresponding light detectors 112, 121.
However, conventional devices such as that shown and described in FIG. 1 have a problem in that, because the conventional optical type touch screen 100 has to use a plurality of light sources 111, 122 and light detectors 112, 121 in order to form the lattice of rays 130, there are a significant costs both in construction and subsequent consumption of electric power by such touch screens. In other words, the costs associated with the power required in order to drive the light sources 111, 122 and light detectors 112, 121 is large enough to render such touch screens as being cost prohibitive in many applications.
Another disadvantage of the conventional touch screens is that the resolution of the touch screens (a degree of precision thereof) are proportionate to the number of light sources and light detectors; thus the costs of manufacturing continue to increase with increased resolution, even when producing such touch screens on a large scale.